New method turns ocean water into drinking water, without waste | Hacker News Reader

New method turns ocean water into drinking water, without waste

rochester.edu

520 pointsspeckx213 comments

There is a fundamental minimum amount of energy needed to desalinate: you can't take less energy to do it,than you could gain back (from osmotic pressure) if you allowed the desalinated water to expand a cylinder containing the residual brine. This is large. This paper is a thermal method, so it doesn't have an electricity input, but to justify their efficiency claim, they should really compare against what you could do by using the same surface area for solar panels, driving a conventional setup. My (limited) understanding is that conventional reverse osmosis is not far from the theoretical optimum, energy-wise, the main difficulties being operational (the membranes need declogging). And of course RO is more expensive than rain.

This paper is interesting, however, in directly producing crystalline salt, which is lower volume than brine and easier to dispose of, maybe even valuable.

If this can be applied to mine effluent, you could replace the maybe with most certainly. Sulfuric acid effluent lakes leech all sorts of valuable metals out of the ground.

Brine is very easy to dispose of: you just pump it back to where it came from. Solid crystalline salt, on the other hand, is a hassle.

"Solid crystalline salt, on the other hand, is a hassle."

Just make prettier-than-Himalayan salt lamps out of it and sell it to hippies. Easy solution.

That only shifts the problem. Now we need an increased supply of hippies that are hard to come by in a low hippie-tolerant environment.

> Brine is very easy to dispose of: you just pump it back to where it came from.

Easy, but not necessarily good for the spot you're pumping concentrated salt back into.

The brine came from the ocean. So just dilute it back to close to ambient salinity using municipal waste water that you are discharging anyway.

> The brine came from the ocean.

Sure, and enriched uranium comes from the ground, but that doesn't mean it's safe to dump it back in after the enrichment process!

> So just dilute it back to close to ambient salinity using municipal waste water…

Wouldn't it generally be easier to process that municipal waste water, as is already fairly common?

The analogy would be if you "un-enrich" it. Then it's safe. Or at least no worse than when you took it out of the ground.

> The analogy would be if you "un-enrich" it.

But you're doing that with the same water you're trying to make in the first place!

You could just dilute it using fresh seawater, if you used enough and (maybe) spread it over a wider area. The amount of water people need for drinking is a relative drop in the ocean.

Brine doesn't necessarily behave the way you imagine.

https://en.wikipedia.org/wiki/Brinicle

https://en.wikipedia.org/wiki/Brine_pool

Blue Planet video of a brinicle, content warning for kind of horrifying death of sea creatures: https://www.youtube.com/watch?v=lAupJzH31tc

And a Blue Planet II video of a brine pool, stronger content warning for much more horrifying death: https://www.youtube.com/watch?v=ZwuVpNYrKPY

You can dilute the brine in a facility before disposing.

Go on. With what?

Seems like you could just dilute it with seawater at like 100:1 ratio and it would be negligible done offshore. We already dump our shit 5 miles out.

100:1 is overkill and energetically very wasteful. It's a fairly straightforward chemical engineering problem.

gasoline

...sea water. You take 10 units of sea water for every unit processed and you'll get a slight increase in salinity.

A phase diagram tells you exactly how far you need to go.

You know this makes more thermodynamic sense than carbon capture, right?

With fresh water, we’ll get it from desalinization! Hey wait a second…

Sarcasm aside, your comment actually works: you can use the freshwater from desalination!

Just wait for the saltwater to come back around in the sewer.

Globally about 70% of freshwater is used for agriculture so less than a third of it will come back around, if it's exclusively for residential/commercial use you might do better but overall not a strategy that balances out

70% of desalinated water wont ever go to agriculture because its too expensive to use for corn. Only very high value crops need apply.

But, so what? 30% sewage is still a strong dilluant... especially when mixed with more seawater

Im shocked how many people cannot grasp that you can dilute brine's salinity arbitrarily close to seawater's with energetically cheap pumps.

> Sure, and enriched uranium comes from the ground

Uranium can also come from the ocean water (there is, apparently, quite a lot of it in there, relatively speaking). Japan experimented with the technology in the nineties, but it really was much cheaper to just mine it from the ground, so they abandoned it.

Japan is also barred from doing own enrichment, being a non-nuclear state. Though, there nevertheless is a dormant set of requisite facilities.

You're wrong. Japan does do their own enrichment, 150k SWUs at Rokkasho with plans to bring that up to 500k SWUs a year soon. If they chose to make.bombs instead of fuel, they could make dozens a year.

That's the dormant plant. Rokkasho-mura plant is officially incomplete for decades, doing tests and upgrades without actual production.

If you think otherwise and you're not wrong, and I think you ARE not mistaken since this isn't the first time someone other than myself mentioned it here, that means they're making bombs because we in Japanese public aren't told about it. There has only been just some routine commentaries from local mayors at most.

I think you might be confusing the Rokkasho Reprocessing Plant (not yet operational, intended for plutonium extraction from spent fuel) and the Rokkasho Uranium Enrichment plant, which has been running at 75 tSWU/year (I think that should be kSWU or tSW) since 2023-08-24 https://www.jnfl.co.jp/ja/business/about/uran/daily/enrichme... 112.5 tSWU/year since 2025-06-26 https://www.jnfl.co.jp/ja/business/about/uran/daily/enrichme... and 150 tSWU/year since 2025-11-20 https://www.jnfl.co.jp/ja/business/about/uran/daily/enrichme...

It's a bit weird though that they have a graph of tons of uranium hexafluoride shipped that shows the last shipment in 2018 and nothing since then.

They also have a large stockpile of reactor grade plutonium. Not the best material for bombs, but workable.

It's about 3 parts per billion. Uranium is about $85/pound, so you'd need to be able to completely process/extract about 40 million gallons of saltwater for $85 to break even. The real cost there is orders of magnitude higher. It's one reason the claim about the Earth having vast amounts of uranium is quite disingenuous. The amount of cost efficient accessible uranium is only enough to last ~1 century at current consumption rates. If nuclear energy scaled up significantly, we'd run out in a matter of decades if not less, or we send the price of uranium skyrocketing and the price arguments would need to be significantly adjusted.

Enriched uranium is perfectly safe to dump but it would be stupid to do so. Fission products are nasty but uranium itself is not, comparatively.

Municipal waste water is a much cheaper way to get desalinated water in the first place though.

except for the pharmaceuticals anyway

Hey, it's free viagra, prozac, progesterone and multivitamin supplements, all in a glass.

There’s some fat fish out there, I hope we can get those guys some Ozempic too

Democrats intentionally killing the fishing industry by giving fish free glp1s and cocaine with your tax dollars!

That’s been a solved problem, engineering-wise, for a while.

The advanced treatment stages take care of it. Between UV, ozone, and nanofiltration, etc. we can remove the pharmaceuticals.

Actually the problem is the water comes out too pure out of a well designed water reuse system, to the point where the mineral content can be too low and you need to add some back in.

Cite for it being solved? All the articles I can find have it as ‘active and growing problem with some potential mitigations which are not universally applied’.

All the recycled water systems I’m aware of still have PCC issues and excess ion contamination problems too still.

Admittedly my knowledge was based on work I did in academia, and I now work in transportation, so I suppose it’s possible I’m in error, but I’d be surprised if much survives the RO stage, and isn’t eaten up by the oxidation stage. My understanding was that the water needs to actually get remineralized to protect the distribution system. And that it’s very devoid of pharmaceutical contaminants by that point. I was unaware of this being an issue in real world potable reuse systems. Though, I suppose different jurisdictions may have different standards. My state was pretty strict.

Maybe, but dumping crystalline salt is even worse to the spot you’re dumping it on.

I wonder. It would have to dissolve, a big block of salt would take a while, kind of like the erosion of cliffs where the salt comes from in the first place. Eh, I guess you're right though, the fish wouldn't like that at all.

It doesn't need to be crystalline salt. Just mix the brine with seawater at a really high ratio of sea water to brine then dump that out. 100:1 ratio should be fine I would guess. Quick search suggests seawater salinity variance is already like 10%-15% or so. Even better if you pipe it offshore where currents will take it and not somewhere that doesn't circulate.

Yes, that's my point: if you're next to the ocean, disposing of brine is extremely easy.

You could put it back into old salt mines.

Even better, just package it up and eat it instead of digging underground and creating more pollution.

It's not every day that industrial waste happens to be not only edible but also tasty. Too tasty, in fact. Salt is addictive.

It’s not going to be pure NaCl though; making Morton salt with it would make sense only if it wouldn’t cost more to process it (net of its resale value) than just disposing of it somewhere not particularly sensitive. I’d propose the Utah salt flats or indeed, kinda love the idea of just sticking them in a salt mine that is all tapped out. If it used to be chock full of salt it seems pretty environmentally fair to make it salty again.

The impurities are exactly what give sea salt from various regions their distinctive flavors and mineral profiles. The salt should be edible as long as it wasn't pulled from seriously polluted waters. It might even sell for a premium.

If you use fat pipes that go a decent distance from shore, diluting your brine with ocean water, you’ll have a negligible impact on the ocean. The problem is if you dump lots of brine in shallow waters. Old designs did have that flaw, but it’s not that difficult to design around this constraint now that we know about it.

IMO this is an issue where NIMBYs are using environmental concerns as a smokescreen to block new desal plants from ruining the vibe at their beachfront property. Rhymes with the opposition against offshore wind farms.

Yeah. Worrying about salt in the sea is like worrying about oxygen in the air. Can too much oxygen in the air sometimes be a problem? Yeah, in some corner cases. Is it a major problem that we can't solve? Not at all.

That makes sense to me. At the same time I know the mediterranean sea is heating up more because it cannot move heat out quick enough. I dont know of any mediterranean air, so I believe more closed water zones would behave different than, lets say, the atlantic ocean.

Isn't it more akin in this case to worrying about too much carbon dioxide in the air?

Why is it akin to that? Doesn't the salt come from the sea in the first place?

A more apt comparison than you realize.

Most of the carbon we spew into the atmosphere came from the air. Ancient plants took it in via respiration.

That still doesn't make it a good comparison. The salt emitted by desalination plants is already in the sea now, it's not salt that went somewhere else.

And the water we take out eventually goes back.

I can probably be convinced pretty easily with some evidence of that, but you’ll never convince the contingent who is convinced it’ll kill sea life at any concentration or location, so, being able to shut them up by saying “we have no wastewater, we load rail cars with crunchy salt and use it for stuff” still has value.

The goalposts will just shift to attack that excess salt instead. It’s like all of the FUD about datacenter water usage while people shove almonds in their mouths.

In Germany, it's the water usage of a Tesla plant vs. the neighboring asparagus farm.

I wish we could reimagine carbon credits to that degree of stringency. You offset a kg of carbon emissions? Let's see that kg.

> The problem is if you dump lots of brine in shallow waters. Old designs did have that flaw, but it’s not that difficult to design around this constraint now that we know about it.

I think that problem was known (and discarded as not important) when the first serious water desalination plants were built.

The city of Corpus Christi, TX is currently considering options for desalination plants—all of which pump their brine into the shallow water inside the bay or the ship channel.

Sounds on brand for Texas.

Actually it's easy and ok. Just mix it with the treated sewage right before it returns. Simple mass action implies the salinity hasn't changed.

But wait! There's water mass loss due to leaky pipes and outdoor pools!

Mixing salt water and brine is perfectly ok. Just use a phase diagram.

that's 200% bullshits. Countries that invested into desalination plants are known to create death zones right where brine is sent back - even if miles from the coast

Someone tell me why this is stupid, which it probably is: Put the desalination plant on a tanker ship and let it do its duty out in the middle of the ocean, then cruise back to port and dispense the water.

Why? Just build mountains out of it and maybe even open a salt-ski park in the tropics for people who don't have snow.

There are salt mountains lining most midwestern freeways as it is for winter.

I just realized that future archaeologists will be tracing our roads using the salt residue!

or just you know.. asphalt residue

Actually I have been thinking about this. Surprisingly straight and long cuts in rock formations might be a real thing to track. In at least some places at least some rock blasting is preferred to get aggregate for road foundations. And these tends to be rather straight and rather steep.

Assuming my constants (35g/kg of salt in seawater, 650k tons of salt dumped by the state of ohio every year, 81 gallons per day of individual domestic water usage) are correct and my napkin math isn't completely buggered, and if we look at the salt as a primary product instead of just waste:

Ohio DOT's use of road salt would allow for fresh water to be provided for somewhere in the neighborhood of 160,000 people.

On one hand, that's nowhere near enough people; it's a small drop in a giant thirsty bucket of water consumption. So we'll still need salt mountains, salt re-distribution vessels, and/or other ways to deal with excess salt.

On the other hand, 160k is a lot of humans. So perhaps we should look into doing things like this anyway.

(But we probably won't. Ohio gets road salt primarily from a mine under Lake Erie that has a very conveniently-located terminus near downtown Cleveland. The mine directly loads trucks, freight trains, and ships...and it's near the point of use already. It's pretty efficient.)

I think I read somewhere that salt can be used as energy storage medium? So we could get both water and batteries for renewal energy.

It’s about thermal storage, you don’t use table/sea salt for that, and you don’t need a lot of salt, because the salt is in a closed loop; it’s not being consumed.

But more thermal storage you want more salt you want, and it's gotta cost something, right?

https://en.wikipedia.org/wiki/Molten-salt_battery

If you read the article you sent me, you'll learn that, just as I said, you don't use sodium chloride, aka table salt, aka sea salt, for these purposes.

A better example are sodium ion batteries, which are about to take off in a big way

https://www.catl.com/en/news/6812.html

In an ideal world that crystalline salt by product could be used to offset any imported or mined salt, further reducing the environmental impact of those operations.

> Solid crystalline salt, on the other hand, is a hassle.

Just put it on your fries.

yeah, if you like to kill everything in a few 100 feet radius and kill some more in the zone of reliance.

this is delusional ecological

Brine might be bad to the place you dump into, but crystalline salt is even worse.

Overall though, it’s just such a tiny concern. Ocean is huge. If we kill everything in a 100 foot radius, that’s 0.0000000008% of the ocean being destroyed. Less than a drop in a bucket.

So, we could just dump it on the salt flats in Utah? Plenty of places are already super salty, so nothing lives there (unless it’s able to handle that).

Oh no, the hassle of managing the raw input for several key industrial processes that is created for free as a side product of MAKING WATER DRINKABLE WITH FREE ENERGY FROM THE SUN is TOO MUCH OF A PROBLEM! Especially considering we could instead murder millions of fish - which we then can’t eat- in the process! This entire technology is doomed!

Come on guys please at least attempt to think what you’re about to type, please, I beg you.

> My (limited) understanding is that conventional reverse osmosis is not far from the theoretical optimum, energy-wise, the main difficulties being operational (the membranes need declogging). And of course RO is more expensive than rain.

RO is about 2-4x the theoretical minimum, depending on how much water you're willing to reject.

Thermal methods require energy, it seems like this substrate is effective at maintaining its solar-thermal absorbing properties better than a material that will attract salts

> Testing their solar-thermal desalination technique using samples of water from the Pacific, Atlantic, and Indian Oceans, Guo and his team were able to make the surface self-cleaning. In other words, it extracted freshwater and directed the remaining salts to the passive region where they could be later collected without reducing the panel’s efficiency.

This is not "large" this is a moderate improvement. Albedo is likely only marginally affected, and the solar power input over area is the same.

Depending on this cost of this process it could very likely be a wash in terms of NPV

Focusing on pure energy efficiency might be missing the point of economic efficiency.

An RO desalination plant needs electric energy to drive the pumps, which might be generated by panels which are 15-20% efficient. So, if you can have cheap thermal desalination panels, they come out ahead even if 6x less energy eficient, you avoid the whole expensive and fragile desalination plant and you gain a low skill, distributed setup.

This is valid for some use cases, but then it needs to be compared with other solar distillation methods, of which there are already a variety at different levels of energy efficiency, complexity, and land use.

ScholarlyArticle: "Extreme salt-resisting multistage solar distillation with thermohaline convection" (2023) https://www.cell.com/joule/fulltext/S2542-4351(23)00360-4 .. https://scholar.google.com/scholar?cites=7551078272963689346...

"Desalination system could produce freshwater that is cheaper than tap water" (2023) https://www.eurekalert.org/news-releases/1002811

ScholarlyArticle: "Highly efficient and salt rejecting solar evaporation via a wick-free confined water layer" (2022) https://www.nature.com/articles/s41467-022-28457-8

"Solar-powered system offers a route to inexpensive desalination" (2022) https://news.mit.edu/2022/solar-desalination-system-inexpens...

I remember the MIT press release. I wonder if they've found any commercial success.

MIT had a spin-out company some years ago doing HDH (Humidification-Dehumidification) desalination.

In thermal cycles, the problem has been in the condensation step. If there is a carrier gas present this inhibits heat/mass transfer at the condenser surfaces. The usual way of getting around this has been to operate the system with no carrier gas, but that requires pressures below atmospheric pressure, requiring strong walls to withstand external atmospheric pressure.

The MIT invention was a bubble tray contactor, where air is bubbled up through trays of progressively cooler water. The water/air bubble interface provides a large surface area at low cost. One of the markets for this was cleaning up brine from fracked wells.

The company, Gradiant, is still around but has evolved to involve a wider range of water treatment technologies (which is very sensible from a business viewpoint, as customers buy complete solutions, not individual technologies). https://www.gradiant.com/

I always thought that if separating water and salt were easy, our bodies would have evolved to do it so that we'd be able to drink sea water and be fine. It must have been so expensive that searching for fresh water was worth it or there were plenty of fresh water that it was never a evolutionary pressure. Evolving kidneys capable of concentrating urine beyond 3 something percent concentration (sea water) perhaps required a massive restructuring of our internal organs and a huge constant energy expenditure, so we kept seeking fresh water.

ps. I have no clue what I'm talking about

Salt water fish can process sea water, no point in evolving for saltier brine if you have oceans of 3% water.

It’s mostly that it takes energy. If fresh water is we drink that. There aren’t a lot of places where only salt water is available so, for most animals, it isn’t worth it to have evolved a way to extract water from salt water.

Animals in the ocean of course do live without fresh water. Some of them just live off of water extracted directly from their food or from metabolizing that food, which produces water. Some animals have specialized cells that excrete salt so that can take in salt water and separate out the salt.

>I always thought that if separating water and salt were easy, our bodies would have evolved to do it so that we'd be able to drink sea water and be fine.

Unfortunately for terrestrial animals, it's just not that simple. Seawater contains a lot of microbial life, some of which can be infectious or toxic. Going to the coastline to drink is potentially hazardous, because it usually means descending a hill on a predictable route which will be attractive to predators. And you need to get pretty far into the water, usually, because of nasty stagnant runoff, which can come from decaying matter that washes ashore, and sand in the surf. That means you risk drowning. Plus, you don't just need the energy for desalination, but the infrastructure (similar problem to real life!), which means more and larger juxtamedullary nephrons in the kidney, which is already a major weak point on the back due to the high blood flow in the kidney. Meanwhile, most of your food contains a lot of water, especially if you're one of the 99.99999% of animal species that doesn't cook it.

This is a weird angle I think? Desalination brine is a real problem, so if you can eliminate that then efficiency is less of an issue (especially given that desalination plants are often in places with a lot of sunlight!).

You don't want to be super duper inefficient but "no waste that has to be dumped back out" feels really big to me

The paper: [1]

They're still at lab scale in glass. They haven't built a usable system, even a small one. The big claim here is that it doesn't clog; capillary action moves the salt out of the active area to another area, where some yet to be developed mechanism removes it. That needs to be demonstrated. If they can come up with something that runs for years without clogging or replacing the active material, that's a real advance.

Laser surface preparation is known.[2] It's useful for roughening smooth surfaces in a very structured way, in preparation for painting. The result is a smooth paint surface. If you sandblast to roughen, the first paint layer is somewhat irregular. Then you need to sand and paint again to get a smooth surface. Laser roughening has been tried for auto painting, but didn't go mainstream. A good question here is whether commercial laser surface prep systems can make the material this new process uses.

[1] https://www.nature.com/articles/s41377-026-02315-4

[2] https://www.youtube.com/watch?v=BKYOglHYo_Y

It reminds me of how the Panama canal was built, and actually the first major attempt failed and they gave up. What they learned for the second attempt was that digging was not the hard(est) part to solve - it was how to move the dirt! So much dirt!

Great book on this BTW: Path Between the Seas. I couldn't put it down.

Fragility is a common problem in surface treatments, sometimes called "nanotechnology". There are super hydrophobic surface treatments that are very effective. They generate a surface which is a forest of tiny sharp points. The surface tension of water is too high to cling to such a surface. You can make something that just will not get wet. The problem is that the points are fragile, and wear destroys the effect.

Another example is ultra black coatings. Those are a forest of tiny black objects arranged so that light gets reflected multiple times and is absorbed. The commercial version is called "Vantablack". It doesn't wear well, but for optical applications such as the insides of camera lenses and telescopes, that's fine.

It's such a good book! Like any dad reading history, I have been annoying my family for years with fun facts I learned in that book. David McCullough's other books like The Great Bridge (about building the Brooklyn Bridge) are also great.

You and I are the same person apparently. Let me tell you about malaria! Or the bends! Or tetanus! Please! Wait, where's everybody going?

Did you know that IBM got its start building the control center for the Panama Canal locks? Did you know that lobbying has been the same since at least the 19th century? That 10% of all of France's population invested in their canal company, but the company was too afraid to tell the people that Panama wasn't flat like the Suez Canal area? And... and... and...

This is an interesting tech, but I have big doubts. In the picture you can see some salt coating the surface. Even just a little seems like too much for this type of system. I really hope they can make this work and scale this up.

This is similar to a MIT press release from 2023.[1] That's another passive solar powered desalinization system that supposedly doesn't clog with salt. The author's paper list has the 2023 paper, but no followup.[2]

Another MIT paper on desalination from 2024 has a more conventional electrically powered system that can adjust its operating speed depending on how much power is coming in. So it can run off intermittent power sources such as its own solar panels.[3] Rather than buffering the energy with batteries, just buffer the water in a tank. This made it to field test and has some efficiency numbers.

It's annoying to see these one-off announcements with no followup. A short note a year later reporting why there's no further work would be useful to later workers.

[1] https://news.mit.edu/2023/desalination-system-could-produce-...

[2] https://drl.mit.edu/publications/journal/

[3] https://www.greenmemag.com/science-technology/breakthrough-m...

The crucial part is that pressure from the capillary action pushes the concentrated brine out onto the non capillary area. unlike fabric the area isn't enclosed so cleaning is easier if the salt starts to accumulate.

Obviously it needs to be cleaned regularly otherwise the salt encroaches into the sensitive bits. However the cleaning method doesn't require dissolving, just scraping.

They are talking about lithium recovery, but there is a less exotic byproduct I'm interested in. One tonne (≈ 1 m^3) of seawater contains about 1.3 kilograms of magnesium, equivalent to about 4 kg of magnesite ore. Typical desal prices are on the order of $1 per tonne. Magnesite ore goes for about $100 per tonne, so the crude magnesium in a tonne of seawater is worth about $0.40, which could account for a substantial fraction of the desalination cost. (These numbers are very rough.)

Now you ask: why don't we just recover magnesium from brines if it's so great? Magnesium recovery from seawater isn't that easy: typically you have to treat it with some kind of alkali (often Ca(OH)2), so the cost is dominated by the extraction process (your alkali is consumed!), and you're competing with a pretty cheap ore. But if you have a solid byproduct, instead of a liquid, the options for magnesium recovery might be a lot more efficient, potentially offsetting the cost.

The fourth-most-prevalent ion, sulfate, might also be interesting, at least in a hypothetical post-petroleum future where sulfur as a byproduct of fossil fuel extraction is no longer "free". Sulfate is also annoying to extract from seawater, but again if we have a solid, the rules change.

As for the "table" salt itself, I think we'd quickly saturate (!) the market.

Calcining Mg(OH)₂ -which is what you find in seawater - converts the soft compound into magnesium oxide, a valuable mineral commonly used in refractories, catalysts, and ceramics.The Chemical Equation: $Mg(OH)_2 \xrightarrow{\Delta} MgO + H_2O$Temperature Requirements: You need to heat the magnesium hydroxide to a temperature range between 500°C and 900°C. Heating at the lower end (around 500°C) yields a highly reactive, porous form of nano-MgO, while heating above 1,200°C creates "dead-burned" MgO used in high-heat industrial bricks.The Yield: The weight of your final MgO product will be roughly 69% of the original Mg(OH)₂ mass, as the evaporated water accounts for the 31% weight difference. Already energy intensive. To get to magnesium ore is another step.

>Calcining Mg(OH)₂ -which is what you find in seawater

I'm not sure what to say, because it looks like you are copy-pasting from Wikipedia or something like that. Anyway, Mg(OH)2 is not found in seawater. Mg2+ is found as a dissociated ion. When you dry it, it mostly becomes MgCl2 with a little MgSO4. Mg(OH)2 is produced from seawater by the alkaline extraction process I mentioned before, and the process in TFA is interesting because it might be better.

Also, nobody would ever make magnesite ore. I referenced magnesium ore prices to estimate the value of the magnesium-as-ore in sea salt, because using finished magnesium prices would be misleading. Magnesium is mostly consumed either as the metal or as the oxide in cements and ceramics.

> : $Mg(OH)_2 \xrightarrow{\Delta} MgO + H_2O$T

At least read what you're pasting

This appears to be the same New Rochester article as 4 days ago with 20 comments.

https://news.ycombinator.com/item?id=48349507

>> The solar-powered system uses specially engineered black metal to absorb sunlight.

The new system replaces the earlier version that used specially engineered death metal.

Which was a big upgrade from the prior system which just used a heavy rock.

Which in turn was a huge upgrade from classical methods

After looking at the paper, this looks like the core result:

“We collected a total of 9.3 g freshwater along with 0.343 g of sea salt from the ABF-STIC with a 9 cm2 surface area over the course of 9 hours. This is equivalent to generating 10.33 liters m−2 of freshwater and 0.38 kg m−2 of sea salt per day. The salinity of the desalinated water is found well below the WHO and EPA standards for safe drinking water.”

However the enclosure system required looks rather complicated and might be sensitive to external temperature (maybe a solar PV-powered cooling loop would help) and I imagine the cost-per-square-meter of the material is rather high, so this looks more like something for emergency response situations or maybe a desal system for a mega-yacht. If it could be scaled the idea is interesting, maybe as lithium separation from concentrated geological brines?

Awesome, love seeing stuff out of Rochester - RIT or UofR or any of the nearby schools.

Totally underrated area for academic pursuits.

Agree! Shout out to the Laboratory for Laser Energetics

UofR physic grad that also worked at the LLE here. Agree Rochester schools are underrated (although admittedly a little biased).

At least in the sciences you have access to lots of opportunities you don’t have at bigger name schools.

They set me up in life in a way that I don’t think would have happened elsewhere.

I had a great time at UR in the early 90’s because they had the most computing hardware per interested student in the country. I was able to relatively quickly work my way up to access to pretty much any system the school owned that I wanted, including the Cray at the LLE.

Indeed, it’s the same university that gave us room temperature superconductors.

Huh? That was University of Utah/Brigham Young University right. That is, if you're referring to Pons and Fleischman.

Pons and Fleischman was cold fusion. https://en.wikipedia.org/wiki/Cold_fusion

I was referring to this scandal: https://www.nature.com/articles/d41586-024-00716-2

RIT is pretty well known as a good school I believe.

As an RIT alum, I tend to agree.

I believe the most efficient method to turn "ocean water into drinking water" is called "rain". We just need to better collect and transport the output of what is effectively the world's biggest solar-powered desalinator.

Well, sometimes it doesn't rain and (at least for coast regions) being able to desalinate can be of critical importance.

Let’s grab a giant pole and catch clouds. I wonder how much liter of water a giant cloud is. I also wonder what a good unit would be for a cloud. Small, medium and large is all I have

Obviously this is region specific, but slowing down water is one of the best ways to have fresh water.

Slow it down from trickling down a slope and you have two things: more vegetation (which also retains water) and more time for that water to penetrate the ground for local wells.

You can completely "terraform" a desertic region https://youtube.com/shorts/cfhbtgon4Nk?is=oAExB5UeMAsShBux

Geography and prevailing winds have conspired to make certain regions devoid of rain, even many that are right next to the ocean. Competition over resources like water are behind a lot of human misery. The more potential solutions for obtaining fresh water, the better.

So crazy question: take a dehumidifier, attach some solar panels, and deploy at scale for non-potable water suitable for crop irrigation anywhere that isn't a desert. Does it work? And if not, why?

What do you mean work? No, because there is no single dehumidifier on the market that will get you enough water, so you are out $80 grand, you could have just paid for water delivery.

It "works" in the sense that this is what 99% of "Get water from air" scams are.

The reason it doesn't actually work is that it is extremely inefficient. Getting water to condense requires you to somehow reject massive quantities of heat. That's fundamental to physics.

Also, literally anywhere a dehumidifier is reasonably effective, is humid and usually doesn't have such dire water problems. Deserts have extremely low humidity and dehumidifiers working in a desert will produce very little water.

Even a good humidifier in a humid environment is burning KW to generate on the order of ten liters of water a day.

There are a couple places on earth that are essentially deserts but have an early morning humid fog roll through regularly, and those places figured out capturing that water in the air long long before we invented the refrigeration cycle.

It is literally cheaper to desalinate.

Maybe you could build giant greenhouses to fill with sea water and let the sun evaporate the water and collect that with a dehumidifier? Still absurdly inefficient. Water has such an obscene specific capacity for heat that any thermal avenue of separating it from something else will use immense energy.

It takes too much energy and produces water too slowly to scale. In general any area with sufficient moisture in the air to explore this also has easier access to rain and ground water.

Great point, in my case in the PNW, the water from my local well is infested with manganese (as in clogging the household plumbing in the absence of a sediment filter) and other contaminants and the water company providing it is owned by private equity. Legally, I can drill my own well for non-potable irrigation, but god forbid I filter and/or chlorinate it for my own household use. So I end up considering options like this, thanks for debunking.

You don't need to chlorinate water from your own well, unless maybe you have a cistern that you are filling for storage.

And who's going to know if you are drinking it or watering your garden?

At the very least I would UV disinfect anything coming from the ground and absolutely make use of a 20 micron sediment filter if only to address cognitive load: Another place, another time, coliform bacteria from the well. Super fun(not).

I vacillate between trusting my well and trusting my RO (10,5,1 micron filters, plus the membrane). But it isn't healthy to drink RO all the time and I don't wanna mess with remineralization.

My well is 100' and 13 years old.

For me I'd do a sediment filter and a charcoal filter and call it good. Send a sample out for analysis a few times a year.

A lot of energy is only a problem if that energy is very expensive.

The good news in a desert: plenty of sunshine. So you can generate a lot of electricity with some cheap solar panels, there is plenty of space to put some down, and there aren't a lot of NIMBYs around to complicate the permitting process for that.

Some desert ecosystems actually depend on condensation with specialized plants and animals harvesting humidity from ocean breeze. Large parts of e.g. the Sahara border on the Atlantic ocean. Lots of water in the air but not a lot of rain. And even if humidity is low, there still is some water in the air usually.

But the simple fact of course is that there is a lot more water in water than there is in air. If you want to extract meaningful amounts of water from air, you need to process a lot of it.

The humid areas where they might work probably already have a lot of water?

The short answer is all those problems have already been solved.

Israel desalinates 75-85% of its drinking water. The problem is political and economic dysfunction.

California for example could be doing widespread desalination with nuclear power and technology from the 1970s. They could also greatly expand reservoirs and waterways, but don’t do it. Very similar to Rome in the 400s, when people were using aqueducts built by a past civilization but lost the ability to construct them.

Nuclear is very expensive per MWh and thus per litre of water generated

Solar on the other hand is very cheap, and you don't need to desalinate 24/7 -- just do it when power is cheapest (which is during the sunny times if you have large amounts of solar, during windy if you have large amounts of wind, etc)

Yield depends on humidity, which varies according to region and season.

It also requires more infrastructure to get yield. In theory all you'd need to have is these etched metal plates, a transparent dome and a source of briny water. (and a cleaning mechanism)

The etched plates creates 100% humidity (probably more as it'll condense out)

If true then this might be indeed a game changer, but numerous academic publications turned out to be unfit for upscaling.

Who all has access to a femto laser? As far as I know these are all patented, and most of those patents (or at the least companies with rights to production) are in the USA, according to a professor who told us so some years ago in university (in central Europe, but he is quite old already, so I am not sure if his information was 100% up to date; but otherwise I do not doubt the validity of his claim made). So someone is going to milk rather than help. Will be interesting to see what happens to that in some years. My current guesstimate is that nothing will really happen or change.

Always wondered why the coast of the Red Sea isn't littered with channels which get flooded with seawater, which then evpporate into glassed ceilings; creating freshwater, and leaving behind salts for mining.

Sand -> Glass -> heated saltwater -> freshwater + minerals -> ??? -> profit?

Combined with some mangrove farms, surely desert coasts are able to support more life.

Wonder if this is scalable tech, and how quickly it can 'process' water. I guess if they're combined with transparent solar panels, it could be quite an epic tech.

If you've ever been to the beach, you can smell the salt air and rotting seaweed and hear the birds.

It's all gonna get on the glass (from above and below), and eventually the salt left behind is going to build up. The salt left behind is very hard on any structure or machinery used to move it which makes repairing the large glass enclosure a pain. All this for a slow trickle of water is generally not worth it.

The Saudis were fucking around with the idea of solar domes at one point. Haven't heard anything about it for a while though (probably due to maths, lol). A shame, I've always been fascinated by Egypt and the empty expanses of nothingness. On long bus journeys around the country, the imagination can run wild.

https://www.solarwaterplc.com/featured-news/whats-inside-thi...

The issue with that idea is very simple - creating those inlets into the desert would risk soil erosion - in the desert. If your objective was to desalinate water, you're much better off using conventional desalination (there's still way more room to work around here first, like better and sustainable membranes, etc.) and offsetting your emissions by locking carbon away in mangrove reserves, which are native to those desert coasts.

Slightly different idea to take Red Sea water, concentrate it, and flow into the Dead Sea to stabilize the water level in the Dead Sea which is a big problem. A billion or so was spent but the project is on hold for some combination of financial, political and environmental issues.

https://en.wikipedia.org/wiki/Red_Sea%E2%80%93Dead_Sea_Water...

I love projects like this. A shame the west has handed over the baton to the Chinese and Saudis when it comes to actually being daring with megaprojects.

Some over stuff whhich are cool to read about:

Redirecting Siberian rivers into Central Asia https://en.wikipedia.org/wiki/Northern_river_reversal

Redirecting Congo basin rivers to replenish Lake Chad https://en.wikipedia.org/wiki/Lake_Chad_replenishment_projec...

Filling in a depression in Egyptian Sahara desert and fllooding it with Mediterrraanean water to generate huuuuuuuuuuuuge hydro https://en.wikipedia.org/wiki/Qattara_Depression_Project

(Similar ideas proposed for Lake Eyre, the lakes in Tunisia, and the Afar Depression in Djibouti, too).

The Saudis aren't "daring" with megaprojects. They're fucking[1] stupid[2]. Saying their megaprojects are "daring" is like saying I'm "daring" for claiming I'm going to build a catapult that will launch me to the moon.

[1] https://en.wikipedia.org/wiki/Trojena

[2] https://en.wikipedia.org/wiki/The_Line,_Saudi_Arabia

A comparison that only works if you say it and sink a few billion into foundations for said catapult.

That’s what daring means. You try things that do not guarantee success. I remember a decade of people shitting on Dubai for all of the crazy projects it was building. It really paid off for them (pre Iran war). They made something out of nothing and still are. What’s stupid about a kilometer high tower? It’s fucking awesome.

Speaking of shitting on Dubai have they built any plumbing yet or are they still trucking their sewage out of town?

Still trucking but that’s another attempt at diminishing some pretty great achievements. Turning a sterile, hot piece of sand into a “destination” isn’t easy but they managed to do it. Do you bring up lead pipes and police violence every time someone talks about the US?

I wonder how many times the UK and USA had to 'be stupid' to achieve some of their best achievements?

When curiosity gets replaced by bureaucracy and regs, you know a civ is dead..

I am wondering if they combined photomolecular effect[1] to make it even more energy-efficient

[1] https://news.mit.edu/2024/how-light-can-vaporize-water-witho...

Nature desalinates seawater all the time in the form of water vapor without using electricity. There must be another way for humans to command and control the release of fresh water out of the ocean for our own needs.

There is, but it takes plenty of energy in one form or another. Nature has the advantage of scale. One kilowatt per square meter over the whole oceans.

> The solar-powered system uses specially engineered black metal to absorb sunlight.

Brutal. 𖤐 \m/ 𖤐

This is a big deal for gulf states, another revenue stream in a the post-fossil world for them. Makes a transition more attractive for them.

Distillation of H2O, where it loses an oxygen molecule and becomes H2, or gains a hydrogen molecule and becomes H2O2.

Probably some of the best news I've seen in a while.

…but needs a specially engineered piece of metal…

What, again?

interesting read

> without waste

...except for the huge piles of salt.

If the salt was not waste, surely people would already be extracting it from the brine and the existing methods would also be "without waste".

Persian Gulf has 20% more salt in water because of the humans which are throwing the oversalinated waste back into the sea. Dehidrated salt may be a big deal for some areas because of no waste into input.

>Persian Gulf has 20% more salt in water because of the humans

I would like to read more about this from an authoritative source.

Through the magic of Googling "Persian Gulf salinity" it seems like it's more that it's a shallow Gulf in a dry area so it has significant evaporation. Desalination does effect it but it's only a few percent of the total evaporation (which is still surprisingly big) and doesn't sound like the main driving factor or an imminent ecological concern.

https://www.frontiersin.org/journals/marine-science/articles...

https://www.sciencedirect.com/science/article/abs/pii/S14635...

I thought the HN-way was to be more charitable than just directly calling out obvious bullshit.

pardon my ignorance. But, all that salt was there already. right? Is it that we have less water there now ?

If salt and water flow in but only water flows out you will be left with salt. Same reason that concentrated brine comes out of a desalination plant, or that the dead sea is what it is.

Huh, looks like they process about 1/500 of the water in it every year. So enough to make a dent in the salinity eventually.

Look at a map. The Persian Gulf is a dead end, and all ocean water flow has to come through the Strait of Hormuz. There's some fresh water coming in from the Tigris and Euphrates rivers, but less each year as that fresh water is captured and used, and as global warming increases evaporation.

The San Francisco bay has to be actively managed for similar reasons. It's a large body of water with a narrow outlet, fed by a river system from which much water is captured. If too little water comes in from the Sacramento River, the delta will turn to salt water. Managing that is what the Bay Model, mentioned recently, is for.

The brine is waste, and the dehydrated salt is also waste. Maybe dry waste is better, but it's still waste.

Lavoisier’s “Traite elementaire de chimie” refers to water electrolysis.

I’m not even going to night clicking on a title that is clearly a load of bullshit.

I suppose you could water down the ocean water it’ll was drinkable, or like just add half a teaspoon of sea water to a cup or drinking water.

Buy all work done eventually decades in to waste heat.

Can we please ban university press releases

why

I'll bite, I'll bite. But first ...

@GP: Instead of a plain complain, it's better to get an interesting discussion to write an explanation of why the post makes no sense, or instead find the good debunking comments and upvote them (there are two or three good comments near the top now).

I try to be that guy (personal hall of shame https://hn.algolia.com/?dateRange=all&page=0&prefix=false&qu... ) but life is too short and I have other things to do IRL.

Also, it's not my area. It's close enough to have a good guess, but in this case for me it's better to let someone else give an accurate reply.

---

Back to this post:

It obviously makes no sense. You have salt water, you extract the water, you have to get rid of the salt. Why waste time reading the details? [There are some interesting technical ideas about new surfaces, more on this later.] Reading the details their brilliant idea is to make salt cubes and sell them. So there is no waste!

When you get rid of the salt using brine, it's easier to transport and dilute the liquid. With solid salt you must scrape it form your high tech surface (without scratching it?!) and now the solid salt is difficult to transport. Also, to sell it you must purify it because it will include nasty things like crabs legs and sea smell.

Once you extracted the 99% of the water, it's difficult to extract the other 1% of the water because it's saturated solution with a low osmotic pressure, vapor pressure and a high boiling temperature. Also, water inside the block of salt is difficult to extract, and you must crush the small blocks.

Salt production is done in big salt lakes areas, where energy is "free". I like to consider it like a huge natural solar panel. You get heat for "free" and dry wind for "free". You must pay for them in an industrial facility. Also, the normal process still requires a lot of manual labor of guys/gals with [mechanical] shovels to makes piles of salt, wait, turn it a few times, wait, turn it a few times, wait, ... and you now have a nasty salt that you still have to purify to be able to sell it.

So they will get salt that is too expensive to sell, and too much of it to flood the market, and if you put it in the garbage can it will be classified as [industrial] waste.

---

The technical part looks interesting, but it's on the bottom of an unrealistic title and first paragraph. The interesting part is about the new surface with nano details and titanium oxide that absorbs Lithium. It sound interesting and they published it so there is some validation of the claim, but after the nonsensical first claims I'd want to take a look at the feasibility details.

---

>> Can we please ban university press releases

> Why?

I work in an university and I expect technical accuracy from the press department of an university. We want people to give us money in exchange of doing real and interesting things. We want people to trust the medical doctors when they give health advice, or a lot of other specialist about other public policies.

A lot of press release of the universities have a lot of exaggerations, burning the trust of the people. Before opening one here, I like to guess what is the real result and what is the bullshit part. I think that a complete ban of university press release here is too much, but I understand why the GP is annoyed.

What about removing oil from water, have we conquered that yet?

you can now extract (like mining) minerals from the ocean, sounds kind of dangerous for the ecosystem maybe? making it profitable to extract magnesium, lithium, salt... we can probably guess how this story goes.

i'm hoping it doesn't scale, honestly.

You're worried we might use all the salt in the sea for some kind of ... salt pyramids, send the water back out through sewers, and consequently leave the world's oceans diluted? That's about 1 followed by 21 zeroes, I think, in liters.

no, just take the water, remove the salt & minerals. Over time it'll dilute. Water falls again in the form of rain, obviously, but not the salt.

You're not worried? If it's for batteries? For sure they'll extract whatever they can.

Right, remove the salt and minerals. We don't need that much salt, so we'd have to build pyramids or something with it. We drink the water, but then it ends up back in the oceans. The reason I mention that part is because if it didn't, if we could destroy the water, then the remaining water would retain the same salinity, and the concern would be that we drain the ocean dry, which is silly (I refer you back to how big it is). But we don't destroy water when we use it, so instead the worry is that we dilute all the world's ocean, which is also silly (I again refer you back to how big it is). We need a lot of batteries, but the sea is not useful as a source of lithium except as a byproduct. Even if it was the only source, the old batteries themselves would soon become a better source, as concentrated stores of lithium compared to the very-much-not-concentrated lithium in the ocean. But anyway the good places to mine lithium are on land (and are dried-up bits of ancient ocean, I think).

(I checked, some deposits are old lakebeds like https://en.wikipedia.org/wiki/Salar_de_Uyuni and others are igneous.)

It's also possible - true, I bet - that all the car batteries and storage batteries 8 billion people could possibly use are equivalent to only a tiny fraction of all the lithium in the ocean, but it would be harder arithmetic to confirm that, as well as being irrelevant on account of land-based mines existing.

Someone above said 4kg of magnesium per ton of seawater. Apparently lithium is 0.18g per ton of seawater.

That still means there's billions of tons of lithium in the seas, though.

I get it. The thing to me is, though, how do you know whether extracting some amount of minerals is irrevocably gonna change the ecosystem for some species or not? If it changes it badly for some, then a chain reaction can of course alter something important.

Can it be, for some species, like changing the formula of the atmosphere's air for us?

You're wildly underestimating the scale of the ocean. If we could extract all our necessary minerals from it rather than mining them that would alleviate a huge cause of environmental damage.

This reads like hyperbole:

> The brine byproduct wreaks havoc on sea life when it’s deposited back into the ocean by raising the salt level and lowering oxygen in the water.

Managing return of concentrated brine should be entirely tractable in the literal ocean.

Sure, but typically desalination plants are located in a single physical place, so a discharge pipe dumping brine 24x7 is bad for all of the things around it, as the local concentration is extremely high.

Seems like you could run a long perforated tube to diminish that effect.

And it doesn't even need to be a rigid pipe. A flexible pipe made out of, say, waterproof fabric, could be cheaply made to extend miles while remaining open due to the pressure of the water pumped into it.

Things left underwater tend to collect things on it which would make this much less porous over time.

I liked the idea of loading it up on a ship that sails out releasing as it goes out and back. Make it solar powered or even go old school with literal sails.

I thought they tend to pipe far out and discharge as far below the surface as possible, since there is a lot of surface life and it is less damaging this way.

Ships (with long submerged pipes) would be prone to weather events and generally less reliable than an installed pipe. Perforation would be prone to clogging from build up so a nonstarter I would expect. Adding flex tubing and a relocation robot would be a maintenance headache as well. Not sure there is an easy optimization.

Ships wouldn't need a long submerged pipe. It'd just need a small hole like a bilge drain or maybe a live well on a fishing boat. Just let the boat cruise around slowly draining back into the ocean.

As for surface life, I'm no oceanographer, but is that really the most vulnerable place? The surface is where fresh water rain meets the ocean, so that would dilute the salinity during storms. However, there's nothing to say that another pump couldn't be pulling from the ocean and mixing the brine into that so it's diluted before and not just pouring brine straight into the ocean

I think your sense of scale is off. 90% of sea life is on the surface. 0.029% of ocean water is replenished from rainfall annually. Desalination concentrates are absolutely toxic to life. The current daily volume of brine discharge would require more than half the tankers in the world to be filled and discharged every single day. They would of course not last long with such a routine.

Is that a total for all of the oceans? I understand that as a whole, rainfall is literally but a drop in the ocean. However, confined just to the local area where the rain is falling, the area’s salinity has to change. Just like adding the the desalinated brine is a minuscule amount compared to the whole ocean, it has large effect locally.

Regardless, it is totally possible to reintroduce the brine back to the ocean in a way to not be a shock to the local area. We have just chosen to make it harder on ourselves for some illogical reason.

In my opinion you are hand-waving away a difficult engineering problem and proposing a naive solution as if it would solve a problem that has already been partially solved, by rejecting all the work that has already been done on it. Don't dump on the surface, don't burn millions of tons of fuel a year to do it, study what has been done and improve on it instead.

If you want to be really clever about it, maybe the ship is powered by the brine.

https://en.wikipedia.org/wiki/Osmotic_power

I like this! Though I’m not sure the math works. That page says ideal efficiency for that system would be something like 0.75 kWh/m^3. Compared to 4000 to 5000 kWh/m^3 of diesel. Now we don’t need to be efficient since the point is to use up our “fuel” and we don’t need to cary cargo for this to make sense but with numbers like that, I don’t think our boat will be able to make enough power to move at all.

I wonder what the linear diffusion gradient would look like for that. Like the perforated garden hoses or whatever for soaking soil. Aquatic organisms grow so quick though very curious on the constraints for something like this.

The short version is brine is weird: it's surprisingly resistant to diffusing and tends to flow more like an immisicible fluid. So you have to put quite a lot of effort into getting it to actually disperse rather then just fall to the seafloor.

That's silly, you'd mechanically mix it with seawater rather than wait for it to diffuse. The concern would be the volume of desalinated water extracted from the local region versus the flux from ocean current. As long as that ratio is acceptable there won't be any long term problem.

Alternatively, in the absence of sensible regulations a cutthroat operator devoid of ethics constructs a plant that dumps concentrated brine in the immediate vicinity because that's the cheapest approach. Then reactionary elements raise talking points about environmental damage and pretend that it's a difficult problem to solve. Business as usual.

Then they should become salt producers too. Win win (win).

depends of course, how easy does the brine dissolve, how long does it take that it is so diluted that it can't do any harm, without that information it's not easy to tell

These are often built near shallower parts along the coast where changes are more pronounced.

I mean.. we really want to permanently desalinate the ocean somewhat too so putting the brine back seems kinda stupid. Put it on land, let it dry, sell some as table salt and dump the rest into abandoned mines.

Excellent idea! The largest abandoned mines I'm aware of are salt mines, which… hang on.

Yea, that's one of the problems. We're literally digging up salt AND the mountains are being eroded to add more salt. The Earth is getting anti-terraformed and we're speeding it up. (Although obviously the fossil fuel situation is a much closer and worse problem)

It kinda depends where it's deposited, right? The expected AMOC collapse is fundamentally about salt imbalance.

The brine thing is just a way to shut down conversation and let people feel superior for claiming there are no solutions to our problems except to reduce our standard of living.

It’s obvious you can safely put salt back into the ocean with enough dilution. I bet a middle schooler could design a system to do it.

Yeah, middle schooler with middle school understanding can design anything. There are plenty of middle school solutions in the comments around. The problem is when they meet real world, beyond their high school level understanding of the issue.

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